1. Field of Invention
The present invention relates to a multi-phase switching regulator and a control method thereof; particularly, it relates to such multi-phase switching regulator and control method thereof wherein a number of active power stage circuits is increased or decreased according to zero current detection.
2. Description of Related Art
A multi-phase switching regulator includes multiple power stage circuits (i.e. multiple phases) and it is often used for supplying power to a central processing unit (CPU). The multi-phase switching regulator is capable of operating at a lower voltage and providing a higher current as compared to a general switching regulator, and it can provide an adaptive voltage positioning (AVP) function. When the CPU operates, the CPU does not always require high current. Therefore, a multi-phase switching regulator for supplying power to the CPU should have a function of phase adding/shedding control of the power stage circuits.
U.S. Pat. No. 6,764,274 discloses a multi-phase switching regulator, which increases/decreases the number of active power stage circuits (active phases) according to the output voltage which is correlated to the output current. According to the operation mechanism of AVP, when the output current increases, the output voltage decrease, and the multi-phase switching regulator increases the number of active power stage circuits to increase the heavy load efficiency. On the other hand, when the output current decreases, the output voltage increases, and the multi-phase switching regulator decreases the number of active power stage circuits to increase the light load efficiency.
U.S. Pat. No. 7,492,134 discloses a multi-phase switching regulator, which determines the number of the active power stage circuits according to the inductor current. When the inductor current increases, the number of active power stage circuits increases. On the other hand, when the inductor current decreases, the number of the active power stage circuits decreases. When the output voltage drops suddenly, the multi-phase switching regulator of U.S. Pat. No. 7,492,134 instantly switches to full phase operation, that is, to increase the number of active power stage circuits to a maximum number, such that an unnecessary over current protection or system damage may be avoided.
US 2010/0191986 discloses a multi-phase switching regulator, which determines the number of the active power stage circuits according to a voltage signal which is converted from an average of a total output current. When the output current increases, the number of the active power stage circuits increases. On the other hand, when the output current decreases, the number of the active power stage circuits decreases.
In the aforementioned prior art multi-phase switching regulators, the number of the active power stage circuits is determined by detecting the total output current or its related signal. However, to operate by such mechanism, the speed (response time) of phase adding/shedding is determined by the speed (response time) of detecting the inductor current. When the speed of detecting the inductor current is too fast, a mis-operation or current level shift may occur due to the incorrect phase adding/shedding. On the other hand, when the speed of detecting the inductor current is too slow, an unnecessary over current protection or system damage may occur.
Besides, in the aforementioned prior art multi-phase switching regulators, when the light load and heavy load conditions occur alternatingly, or when currents flowing through the power stage circuits are uneven one from another, the aforementioned prior art multi-phase switching regulators cannot respond immediately to operate at an optimum balanced point, which results in unnecessary power consumption.
In view of above, the present invention proposes a multi-phase switching regulator and a control method thereof, wherein the number active power stage circuits is increased or decreased according to zero current detection.